(1) Field of the Invention
The present invention relates to a process for the preparation of a diene type polymer rubber and to a modified diene type polymer rubber. More particularly, the present invention relates to a process for the preparation of an improved diene type polymer rubber having an excellent rebound and showing no change of physical properties with the lapse of time, and to this improved diene type polymer rubber.
(2) Description of the Related Art
Recently, requirements for a reduction of the specific fuel consumption and an increase in running safety have become very severe, and to satisfy these requirements, the development of a rubber material having a small rolling resistance (corresponding to a high rebound as a characteristic of the rubber material), a high wet skid resistance, and a high ice skid resistance is needed as the rubber for an automobile tire tread. Furthermore, since tire tread meeting the requirement for a reduction of the specific fuel consumption is designed by sacrificing its abrasion resistance to a certain extent, the demand for an improvement of the abrasion resistance has increased. Nevertheless, it is difficult to satisfy all of these requirements simultaneously, and in general, the wet skid resistance requirement is contradictory to other required properties, such as rolling resistance, ice skid resistance and abrasion resistance. Accordingly, various processes for modifying polymers have been proposed as the means for maintaining a good balance of these characteristics. For example, a styrene/butadiene block copolymer composed of blocks having different glass transition temperatures (Japanese Unexamined Patent Publication No. 60-192739) and an integral rubber having a sequence distribution (K.H. Nordsiek: American Chemical Society, Rubber Division, 125th Meeting, #48, 1984) have been proposed.
The present inventors previously found that if a diene type polymer having an active alkali metal and/or an active alkaline earth metal at terminals of the polymer chain is reacted with a compound having a linkage ##STR2## (in which M stands for an oxygen atom or a sulfur atom) in the molecule to introduce a specific atomic group in the polymer, the rebound is greatly improved (see U.S. Pat. No. 4,647,625). Subsequently, it was found that not only the rebound but also the abrasion resistance and ice skid resistance are improved by introducing this atomic group into a diene type rubber polymer. Naturally, the effect of improving the rebound, abrasion resistance and ice skid resistance is enhanced with an increase of the addition ratio of the above-mentioned atomic group. Accordingly, the optimum effect is obtained when the above-mentioned atomic group is introduced at all of the terminals of the polymer chain.
A functional group-containing diene type polymer rubber obtained by reaction with a compound having a linkage ##STR3## (in which M stands for an oxygen atom or a sulfur atom) has a problem in that, when the rubber is allowed to stand for a long time, even at room temperature, a rise in the Mooney viscosity thereof occurs. It is known that an aliphatic or alicyclic primary amine can overcome this problem (see Japanese Unexamined Patent Publication No. 63-6034), but it is impossible to completely control the rise of the Mooney viscosity by this process, and if the amount of the amine compound added is increased to enhance the control effect, scorching is likely to occur.